Today artificial joints are used to replace finger joints like the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints, for example in case of accidents or diseases such as arthritis. For use to replace toe joints it is in particular the metatarsalphalangeal joint and the proximal phalangeal joints.
Such artificial joints have been known for some time and a number of different types are employed, as exemplified by patent document DE10354601 B3 which discloses an artificial joint with anchoring shafts that are provided with threaded cutters for attaching the joint to the bone of a patient. Other prior art is reflected by e.g. DE19628476 A1, EP2057971 A1 and U.S. Pat. No. 5,147,386.
The techniques described by the exemplified patent documents allow a flexing motion and some displacement of varying amounts. However, the characteristics of a human joint are not always successfully replicated. In particular, the human metacarpophalangeal joint has the ability to flex in one plane when the finger is curled. The human joint can also endure lateral movement and twisting to a slight degree. Additionally, a form of longitudinal play is possible along the length of the phalangeal joint. These four directions of motion have been difficult to achieve in an artificial joint while still ensuring that the joint is durable, easy to assemble and capable of allowing an optimal bone-to-implant interface that is easily put into the human body, and which best replicates the joint that it replaces.
Typically there is a trade-off between durability of the artificial joint and the replication of the joint that the artificial joint is replacing, and it is believed that present artificial joints can be improved in the sense that a more optimal combination of durability and replication of the joint to be replaced can be obtained.